1. Field
The present invention relates generally to data transmission with a wireless communication device. More specifically, the present invention includes embodiments for pre-distortion in envelope tracking systems.
2. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, 3GPP2 Ultra Mobile Broadband (UMB) systems, and orthogonal frequency division multiple access (OFDMA) systems.
In a communication system, a transmitter may process (e.g., encode and modulate) data. The transmitter may further condition (e.g., convert to analog, filter, frequency up-convert, and amplify) the data to generate an output radio frequency (RF) signal. The transmitter may then transmit the output RF signal via a communication channel to a receiver. The receiver may receive the transmitted RF signal and perform the complementary processing on the received RF signal. The receiver may condition (e.g., amplify, frequency down-convert, filter, and digitize) the received RF signal to obtain input samples. The receiver may further process (e.g., demodulate and decode) the input samples to recover the transmitted data.
A transmitter typically includes a power amplifier (PA) to provide high transmit power for the output RF signal. Ideally, the power amplifier should be linear, and the output RF output should be linearly related to an input RF signal. However, in practice, the power amplifier typically has static nonlinearities as well as memory effects, as described below. The nonlinearities and memory effects of the power amplifier may generate distortion in the output RF signal, which may degrade performance.
A need exists for enhancing pre-distortion within a wireless transmitter. More specifically, a need exists for embodiments related to power amplifier pre-distortion in envelope tracking systems.